Spray-reacted particulate carboxylic polymer-inorganic base compositions



United States Patent 3,453,245 SPRAY-REACTED PARTICULATE CARBOXYLICPOLYMER-INORGANIC BASE COMPOSITIONS Frank J. Glavis,,Rydal, Pa.,assignor to Rohm & Haas Company, Philadelphia, Pa., a corporation ofDelaware No Drawing. Filed June 29, 1965, Ser. No. 468,128 Int. Cl. C08f47/02, 15/40 US. Cl. 26078.5 3 Claims ABSTRACT OF THE DISCLOSURE i Thepresent invention is concerned with the conversion of aqueousdispersions of water-insoluble emulsion copolymers of an acid monomerinto a dry, finely-divided powdered form to provide a water-solublecomposition formed of the water-insoluble acid copolymer and a base orto provide a readily redispersible dry composition in which the amountof base (including any uncombined as well as any combined with the acidcopolymer) is less than the amount required to render the partiallyneutralized copolymer obtained on dispersion completely watersoluble. Inthe latter case, before or after redispersion additional basic materialmay be added to obtain a clear polymer solution.

US. Patent 2,566,149 discloses the preparation of granularpolymethacrylic acid by the spray drying thereof. The polymethacrylicacid, of course, is of watersoluble character.

In contrast with the patented procedure, the present invention isconcerned with the production of a watersoluble composition in drypowdered form from an aqueous dispersion of an emulsion copolymercomprising acid units which copolymer is of water-insoluble character.In accordance with the present invention it has been found that a dry,powdery, water-soluble composition can be formed by simultaneously spraydrying the aqueous dispersion of water-insoluble copolymer and anaqueous solution of an alkaline compound of an alkali metal, the spraydrying being carried out in zones of a heated air stream which areadjacent and preferably partially overlapping or essentially of the sameextent so that at least a portion of the zone in which the polymer isspray dried merges with a portion of the zone in which the alkali metalbase is spray dried.

Any suitable equipment for effecting spray drying may be employed. Forexample, the equipment may comprise a vertical duct in which there isdisposed a spray head or nozzle provided with a plurality of feed ducts,one or more of which is supplied with the aqueous polymer dispersion andone or more of which is supplied with the alkaline solution.Alternatively, instead of the spray head or nozzle just described, theremay be more or less concentrically located within the duct a verticalshaft carrying at its lower end a pair of small discs spaced axiallyfrom each other along the shaft by a short distance so that a feed pipefor the aqueous polymer dispersion may direct such dispersion to the topsurface of the upper rotating disc and a feed pipe may extend betweenthe discs for feeding the alkaline solution to the lower disc. The discsmay have diameters ranging from about an inch to 6 inches and they maybe spaced apart by about half an inch to an inch or more. The shaft maybe driven at high speeds such as from a thousand to 60,000 r.p.m.

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In either the spray or disc type of system, the heated air may be passedin either direction within the main duct, that is from the top to thebottom or from the bottom to the top. The spray nozzle or discarrangement may be mounted centrally relative to the height of the mainduct or it may be mounted at the top thereof or even near the bottomthereof. Depending upon the speed of the flow of heated gas within themain duct, the dried powders may be carried out the top of the main ductby an upwardly flowing gas stream or it may be carried downwardly andout of the main duct by the downwardly passing stream of heated gas. Thedischarged powder carrying gas stream can then be passed into a suitableseparator such as the typical cyclone type. If the rate of flow of theheated gas stream is relatively low, the powder may simply descend inthe main duct to the bottom thereof which may be provided with asuitable collector. These types of equipment are well known and it is tobe understood also that any other suitable equipment may be used tocarry out the process hereinafter described.

The emulsion copolymers may be those having any molecular weight andcontaining from 3% to 70% by weight of acid units in the copolymer. Theacid component may be derived from acrylic acid, methacrylic acid,itaconic acid, aconitic acid, maleic acid, fumaric acid or any otheracid monomer having a group of the formula H C=C or -C(H)=C The acid maybe copolymerized by any conventional emulsion polymerization procedurewith 30 to 97% by weight of at least one other ethylenically unsaturatedmonomer having a group H C=C Examples include the nitriles and esters ofacrylic acid or methacrylic acid with an alkanol having from 1 to 18carbon atoms, vinyl esters of saturated aliphatic acids having from 1 to18 carbon atoms, vinyl aromatic hydrocarbons such as styrene, any of thevinyltoluenes, vinyl chloride, vinylidene chloride, ethylene, propylene,and isobutylene. Examples of the acrylic esters include methyl acrylate,methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate,Z-ethylhexylacrylate and methacrylate, lauryl acrylate and methacrylateand stearyl acrylate and methacrylate. Examples of vinyl esters includevinyl acetate, which is preferred, vinyl propionate, vinyl laurate andvinyl stearate. Besides the monomers of essentially hydrophobiccharacter just described, the copolymers may contain hydrophilicmonomers when the content of acid relative to the content of hydrophobiccomonomer or comonomers is insuflicient even with the hydrophiliccomonomer to render the polymer water-soluble. Examples of suchhydrophilic monomers include acrylamide, methacrylamide, N-methylolacrylamide, 2-hydroxyethyl acrylate, and dimethylaminoethylmethacrylate.

The concentration of the polymer dispersion is not particularly criticalbut ordinarily the emulsion polymer may be produced at relatively highconcentrations from 35 to 60% solids so that the concentration of thedispersion supplied to the spray equipment may be from as low as 5% to60% solids. However, it is ordinarily not economical to use the polymerdispersions at a concentration lower than 10 or 15% by weight so thatpreferably the solids concentration of the polymer dispersion assupplied to the spray equipment should be above 15% and may range up toabout 48%.

As the base solution there may be used an aqueous solution of'an alkalimetal hydroxide or carbonate, such as those of sodium, potassium orlithium, or ammonium carbonate and the concentration may be from 10% to40% within the saturation limits. It is disadvantageous to use too higha concentration in either the polymer dispersion or the base solution inthat the dried components tend to be of larger particle size and not aswell distributed among each other in the dry product.

The temperature of the gaseous atmosphere passed through the main ductinto which the aqueous polymer dispersion and the base solution aresprayed may be from about 100 C. to 300 C. at the point of introductioninto the main duct and the outlet temperature may be from about 35 C. to125 C. The rate of flow of the gaseous atmosphere through the chamber iscorrelated with its temperature to assure that under the conditions ofspraying the atomized droplets undergo substantially completeevaporation before the dried particles can come into contact with theinternal surface of any confining walls and specifically that of themain duct. 'In other words, the particles are dried sufficiently so thatthey are not tacky and do not stick to the walls of the equipment.Depending upon the particular polymer and the temperature at which itsoftens, the temperature of the gaseous stream is selected to avoidexceeding the melting point of the polymer, as it approaches the wallsor is discharged through the outlet of the main duct. Again this is toprevent adhesion of fused polymer to the walls.

The gaseous atmosphere may simply be air or in the event that thepolymer may tend to deteriorate in the heated air, an inert gas may beused instead such as nitrogen, carbon dioxide, helium or the like.

The polymer dispersion may be preheated as it approaches the nozzle ordisc to a temperature below the boiling point. Similarly, the basesolution may be preheated. The temperature to which these dispersionsmay be preheated may be from 30 to 95 C.

The amount of base in the alkaline solution preferably does not exceedthe stoichiometric equivalent of the acid in the copolymer. However alesser proportion may be employed such as from about 50% of thestoichiometric equivalent to 95% or more. Preferably, at leastsuflicient base is included to assure that the particular acid copolymerwith which it is used is rendered water-soluble when the acid groups areneutralized by the proportion of base supplied.

The product is believed to contain a mixture of fine particles of thebasic material such as caustic soda, finely divided particles of acidpolymer, and finely divided particles of at least partially neutralizedacid polymer. These components are so intimately and thoroughlydistributed among themselves in the product, that when the product isintroduced into water, complete solution occurs quite rapidly.

The advantages of the present invention over the normal procedures forproducing a water-soluble salt of a waterinsoluble acid copolymerinclude:

(1) The avoidance of excessive viscosity and/or coagulation commonlyobtained when an acid copolymer dispersion is supplied with sufiicientalkaline material to neutralize the acid groups therein.

(2) Avoidance of the difficulty of removing water from viscousmaterials.

(3) Elimination of a grinding step whether performed on a wet or drymaterial.

(4) The present invention makes it possible to provide economically adispersible acid polymer composition while avoiding coagulation andthickening resulting from pre-mixing base and acid polymer in an aqueousmedium.

The powdered composition may be used for the sizing of textiles, paper,and the impregnation of leather. It may be used as an adhesive in itsown right by the addition of a small amount of water. It may also beused as a sealing composition. For this purpose it may be combined witha large proportion of filler materials such as whiting, clay, barytesand the like. It may be compounded with other materials such asaminoplasts, phenoplasts, cellulose esters or ethers, poly(vic-epoxy)resins, and natural and artificial latices of rubber and syntheticemulsion polymers of rubber type or of vinyl or acrylic esters, etc.

To obtain a free-flowing, powdered product which is not tacky andadhesive so that it does not adhere to the walls of the spray equipment,it is preferred that the acid 4 polymer have a T, value of at leastabout 50 C. when determined at 300 kg./cm. The T value referred to isthe apparent second order transition temperature or inflectiontemperature which is found by plotting the modulus of rigidity againsttemperature. A convenient method for determining modulus of rigidity andtransition temperature is described by I. Williamson, British Plastics23, 87-90, 102 (September 1950).

To assist those skilled in the art to practice the present invention,the following modes of operation are suggested by way of illustration,parts and percentages being by weight and the temperatures in C. unlessotherwise specifically noted.

(1) An aqueous dispersion or latex (40% solids) of a water-insolublecopolymer of 40% ethyl acrylate, 45% methyl methacrylate, and 15%methacrylic acid prepared by emulsion copolymerization at 90-95 C. indeionized water containing about 0.3%, based on monomer weight, ofsodium lauryl sulfate and 0.15%, based on monomer weight, of ammoniumpersulfate (the latex having a pH of 1.6-2.0, a viscosity of 15-25 cps.,and a viscosity average molecular weight of about 150,000) is dilutedwith deionized water to 35% polymer solids, and a solution of grams ofsodium hydroxide (representing of stoichiometry, based on the acidcontent of the polymer) in 300 grams of deionized water is prepared as asecond feed. The latex is then fed through three of four atomizingnozzles of a spray drying unit, the rate of flow main tained by a pump.Simultaneously, the caustic solution is pumped at a proportionate rateand atomized through the fourth nozzle, so that the two feed streams areintroduced into the drying chamber at a proportionate rate. The latex isintroduced at a rate of about 70 grams per minute, the caustic solutionat about 7.7 g./min., and the drying air is fed in at a temperature ofC. and at a rate of 50 c.f.m. (cubic feet per minute). This provides anoutlet air temperature of 65 C. and permits the collection of theproduct as a fine, white, free-flowing powder. This product powder has amoisture content of 2.0%, a bulk density of about 0.4, a 5% aqueoussolution pH of 7.5, a 5% solution viscosity of about 20 cps. Theintrinsic viscosity of the polymer is essentially unchanged after thespray drying operation, and the acid carboxyl (including bothneutralized and unneutralized) content of the copolymer is found to be15.5%, essentially the same as the acid concentration of the initialmonomer mix in the polymerization.

(2) Procedure (1) is repeated except that the latex is fed at a rate of50 g. per min., the caustic solution is replaced by a solution of 171 g.of ammonium carbonate in 750 g. of water which is fed to the spraynozzle at a rate of about 18.2 g. per minute.

(3) A 40% polymer solids latex containing a copolymer of 50% ethylacrylate, 17% methyl methacrylate, and 33% acrylic acid obtained byemulsion copolymerization as in 1) above is fed to the lower of twointegrally joined centrifugal discs rotating at 5,000 rpm. at a rate of60 g. per min. and a solution of 420 g. of sodium carbonate in 1,200 g.of water is fed to the upper disc at a rate of 28.5 g. per min. Dryingair is fed from below into the chamber surrounding the discs at C. at arate of 30 c.f.m., the effluent air leaving the top of the chamber atabout 62 C. The white, dry, free-flowing powder is collected from thebottom of the chamber and is readily dissolved in water.

(4) A copolymer latex is prepared by the method of (1) above but with amonomer mix consisting of 30 parts of ethyl acrylate and 70 parts ofrnethacrylic acid. The polymer latex is diluted to a polymer content of20.0%. Two supply systems are provided, one with 1,000 parts of the 20%polymer latex and the other with 88.4 parts of sodium carbonatedissolved in 1,000 parts of deionized water. These two supplies are thenfed, simultaneously and proportionately, to separate atomizing discs ofa spray drying unit equipped with two, rotating, flat discs, fixedlymounted on a common shaft one above the other with a separation of aboutone-half inch. The discs have a diameter of 4.75 inches and are rotatedat 24,000 r.p.m. Heated air is passed over the atomizing discs at a flowrate of about 50 c.f.m., and the inlet air temperature is maintained at130 C. The feed streams are added at a rate of 5*060 ml. per minute, anda fine-free-flowing powder is obtained as the product, with an outletair temperature of 4550 C. The product is readily soluble in water andgives a 3% solution with a viscosity of 10,000 cps.

(5) A 35.1% solids polymer latex is made as in (1) above from a monomermix consisting of ethyl acrylate: methyl methacrylatezmethacrylic acid,in the proportions 47.5 :49.5 :3. Two feeds were prepared: (a) 600 partsof the 35.1% polymer latex, and (b) 4.2 parts of sodium carbonate in 300parts of de-ionized water. As in (1), these two supplies were fedsimultaneously and proportionately over a period of fifteen minutes,with the conditions and equipment for spray drying being those listed in(1) above, except for the inlet air temperature (125 C.) and the outletair temperature (45 C.). The polymer gives an approxiamtely neutralsolution (pH 8) in water.

(6) The process of (1) above is repeated except that the polymer isprepared from a monomer mixture consisting of ethyl acrylatezmethylmethacrylatezmethacrylic acid, 50:17:33. The polymer has an intrinsicviscosity in acetone at 30 C. of 1.5 deciliters per gram. The two feedsupplies consist of (a) 1,000 parts of the polymer latex at 40% polymersolids, and (b) 54 grams (90% of stoichiometry relative to acid in thecopolymer) of sodium hydroxide dissolved in 250 parts of water. With theother spray drying conditions as described in (1) above, the inlet airtemperature is held at 165 C. while the outlet air temperature is 65 C.The free-flowing powder obtained as product dissolves in water toprovide a 5% aqueous solution with a pH of 7.5 and a viscosity of 500cps.

(7) The procedure of (1) above is repeated with the polymer latexprepared from ethyl acrylatezmethyl methacrylatezrnethacrylic acid,40:45: 15. The polymer has an intrinsic viscosity in acetone at 30 C. of0.17. The two feeds for the spray drying step consist of (a) 1,500 partsof the 30% polymer latex and (b) 40 grams of sodium carbonate dissolvedin 500 parts of water. The two feed streams are introducedsimultaneously and proportionately under the conditions of (1) above,except that the inlet air temperature is 130 C. and the outlet airtemperature is 60 C. The product gives a clear aqueous solution with a5% solution pH of 8.3 and a viscosity of 15 cps.

(8) The process of (7) above is repeated exactly, except that the feedsupply b) consists of 36 parts of ammonium carbonate in 500 parts ofwater. The product is a freefiowing white powder which gives a neutralaqueous dispersion with a pH of 6.8 and a viscosity of 10 cps.

I claim:

1. A process of producing a dry, particulate, watersoluble compositionwhich comprises passing a stream of gas heated to a temperature of about100 C. to 300 C. through a channel, dispersing a stream of an aqueousdispersion, having a concentration of 10 to 48% solids, of a waterinsoluble emulsion copolymer, containing 3 to of acid groups in thecopolymer and derived from an a,,8-ethylenically unsaturated carboxylicacid and another ethylenically unsaturated monomer, into a spray ofatomized droplets in a zone traversed by the gas stream within thechannel, simultaneously dispersing a stream of an aqueous solution of analkali metal hydroxide or carbonate or ammonium carbonate having aconcentration of about 10 to 40% by weight into a spray of atomizedalkaline droplets in a zone traversed by the gas stream within thechannel, at least a portion of the latter zone merging with a portion ofthe first-mentioned zone so that copolymer-containing droplets makecontact with alkaline droplets, the water in the droplets is evaporated,and essentially dry particles of copolymer, particles of hydroxide orcarbonate, and particles of at least partially neutralized copolymer areproduced and thoroughly mixed together in the channel, the amount ofhydroxide or carbonate dispersed being at least 50% but not above thestoichiometric equivalent of the carboxylic acid groups, and thenseparating the mixed powder from the gas stream.

2. The process of claim 1 in which the acid is selected from the groupconsisting of acrylic acid, methacrylic acid, itaconic acid, aconiticacid, maleic acid, fumaric acid, or any other a,fi-ethylenicallyunsaturated carboxylic acid having a group of the formula H C=C or ormixtures thereof, the comonomer in the copolymer comprises an alkylacrylate or an alkyl methacrylate, or mixtures thereof, and thecopolymer has a T value of at least 50 C. when determined at 300 kg/cm3. The process of claim 2 in which the polymer is a copolymer of ethylacrylate or methyl methacrylate or both with acrylic acid or methacrylicacid or both.

References Cited UNITED STATES PATENTS 2,607,762 8/1952 Bowen 260-78.52,566,149 8/1951 Strain 260- 2,763,633 9/1956 Gray 26078.5

JOSEPH L. SCHOFER, Primary Examiner.

STANFORD M. LEVIN, Assistant Examiner.

US. Cl. X.R.

